Glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) is an enzyme, which catalyzes the release of D-glucose from the non-reducing ends of starch or related oligosaccharide and polysaccharide molecules. Glucoamylases are produced by several filamentous fungi and yeast, with those from Aspergillus being generally most important for commercial purposes.
Commercially, glucoamylases are used to convert starch containing material, which is already partially hydrolyzed by an alpha-amylase, to glucose. The glucose may then be converted directly or indirectly into a fermentation product using a fermenting organism. Examples of commercial fermentation products include alcohols (e.g., ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, lactic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid); ketones (e.g., acetone); amino acids (e.g., glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones, and other compounds which are difficult to produce synthetically. Fermentation processes are also commonly used in the consumable alcohol (e.g., beer and wine), dairy (e.g., in the production of yogurt and cheese) industries.
The end product may also be syrup. For instance, the end product may be glucose, but may also be converted, e.g., by glucose isomerase to fructose or a mixture composed almost equally of glucose and fructose. This mixture, or a mixture further enriched with fructose, is the most commonly used high fructose corn syrup (HFCS) commercialized throughout the world.
The end product may also be a commercial feedstock, fed to agricultural animals. Furthermore, glucoamylase has significant applications in food, textile and pharmaceutical industries. In the food industry for an example, glucoamylase is used to improve bread crust color and produce low-calorie beer. Another key application of glucoamylase is as a digestive aid when used together with a cocktail of other enzymes.
However, there remains a need in the art for variant glucoamylases with increased activity, thermoactivity, thermostability and pH stability. The present invention meets this need and provides variant glucoamylases with improved properties compared to a parent glucoamylase.
It is an object of the present invention to provide variant glucoamylase enzymes having glucoamylase activity and polynucleotides encoding the variant glucoamylase enzymes and methods of using the variant glucoamylase enzymes in various processes.